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2.2 Ideal occlusion and normal occlusion

An ideal occlusion is a hypothetical theory based on the anatomy of the teeth and rarely noticed in nature. The theory is utilized to a condition when the skeletal bases of maxilla and mandible are of the appropriate size relative to each other and the teeth should be in a proper relationship in all three planes of space at rest (McDonald and Ireland, 1998).

Normal occlusion according to Houston (1992) was an occlusion within the deviation of the ideal occlusion but still accepted aesthetically or functionally. It was not possible to identify accurately the limits of normal occlusion as long as there was no indication that an anomaly could be harmful to the patient (Houston WJB, 1992).

10 2.3 Malocclusion

Malocclusion can be defined as deviation from normal occlusion which is considered as one of the most prevalent oral health problems (Bhardwaj et al., 2011; Mtaya et al., 2009). It is relatively a common oral health issue that may lead to masticatory, aesthetics, psychological, and social problems (Das and Venkatsubramanian, 2008).

Malocclusion can be further described as the relationship of the dental arch in relation to the normal occlusion which presents in any of the three planes of spaces; vertical, transverse, and anteroposterior. It can also be described as misalignment of individual teeth in each arch whereby the teeth may take a position away from the smooth curve of the arch; where they can be displaced, tipped, rotated, supraocclusion, infraocclusion or transposed (Proffit, 1986).

Malocclusion has an important negative influence on both children and adults (Graber et al., 2016; Shaw et al., 1980) and can cause speech problem, chewing difficulties and psychosocial suffering (Grimm, 2004; Petti and Tarsitani, 1996), periodontal complications and temporomandibular joint disease (Geiger, 2001), bruxism (Ghafournia and Tehrani, 2012), headache (Komazaki et al., 2014), On the bright side, early development of malocclusion can be predicted which may assist orthodontist in developing management strategies taking full advantage of the active growth phase (Proffit et al., 2000; Vig and Fields, 2000).

11 2.3.1 Classification of malocclusion

Several types of classification of malocclusion have been generated for numerous purposes. The requirements for clinical categorization can differ from those of epidemiology (Houston WJB, 1992). Some types of classification of malocclusion have been described based on:

a) Epidemiological data collection

Determination of malocclusion was established for epidemiological data collection and to regulate the technique of assessing and illustrating all occlusal trait within a population (Baume and Maréchaux, 1974; Bezroukov et al., 1979; Björk et al., 1964)

b) Priority treatment need - dental health

Handicapping Labiolingual Deviation Index (Draker, 1960), Occlusion Index (Summers, 1971) and Index of Orthodontic Treatment Need (Brook and Shaw, 1989) which are elements of dental health components were established to evaluate the need for treatment based on dental health in a population so that priority can be allocated to chosen cases when resources were restricted.

c) Priority treatment need-aesthetic

Index of Orthodontic Treatment Need (Brook and Shaw, 1989) taken into account aesthetic component which was acquired in response to social science reviews that highlighted the significance of aesthetic damage on the patient’s psychological aspect.

d) Occlusal classification

There are two methods of measuring the occlusal classification; Angle’s classification according to the first permanent molar relationship (Angle, 1899) and the British Standard Institution based on incisor relationship (British Standards, 1983), which


then provide an explanation of malocclusion with permitted communication between physicians.

e) PAR Index

Peer Assessment Rating Index (PAR) was utilized to contrast pre and post-orthodontic treatment reports by using (PAR) Index component and registered the superiority of the consequences of different treatment strategies (Richmond et al., 1992). This Index component was used for scoring the anomalies in upper and lower anterior teeth such as crowding, spacing and impacted teeth, buccal occlusion by utilizing all three planes of space which recorded from the canine to the terminal molar for the anterior-posterior and vertical dimension but the canine is excluded from the transverse dimension. Overjet is measured from the most prominent incisor; overbite is measured in relation to the lower incisors with the greatest coverage by an upper incisor. For an open bite recorded by the greatest space between the incisal edges. The centerline divergence is measured in relation to the lower central incisors (Green, 2016).

f) Dental arch relationships

One of the classifications is GOLSON Yardstick (Great Ormond Streat London and Oslo) procedure which was established for classifying dental arch relationships in children with unilateral complete cleft lip and palate (UCCLP) observed in the mixed dentition and permanent dentition (Mars et al., 1992). This can also be used to plan surgery and its outcome as early as 5 years of age (Atack et al., 1997).

13 2.3.2 Aetiology of malocclusion

The aetiology of different types of malocclusions are complicated and varied which includes both environmental factors and genetic factors. Environmental factors such as sucking habits have been accompanied with anterior open bite and posterior crossbite (Larsson, 1986). Most often, a combination of both genetic and environmental factors influenced the developing dentition and determined whether a person will end up with malocclusion (Vázquez-Nava et al., 2006; Zicari et al., 2009).

The genetic factors such as genetic syndromes and congenital development may cause a defect of embryologic growth, admixture, and breeding which may produce a reduction in tooth size and jaws which in turn may create tooth size and jaw discrepancies (Proffit, 1986). Furthermore, the mouth breathing was showed the correlation with malocclusion which found that alterations on craniomaxillofacial, generally caused by abnormal mandible displacement and following dysmorphism of the oral structures and altered posture. The causes of mouth breathing are categorized as either inherited or acquired. The previous consist of; choanal atresia, nostril atresia, and nasal septum deviations. The last included; rhinopharyngitis, allergic rhinitis, nasal polyposis, chronic sinusitis, chronic adenotonsillitis, chronic hypertrophic rhinitis, adenotonsillar hypertrophy, malignant and benign tumor’s (Zicari et al., 2009).

2.3.3 The measurement of the occlusal trait

In reporting and determining malocclusion, it is important to determine the prevalence and severity amongst the various population, because it was documented that many of the previous results of epidemiological research were different due to the dissimilar assessment of the features recorded. Occlusal traits can be evaluated directly from the


mouth or indirectly on a study cast or dry skull (Lavelle, 1976). The methods used for recording the occlusal traits can be divided into quantitative and qualitative measurements (Tang and Wei, 1993).

Quantitative methods are beneficial in describing the deviation of an occlusal trait such as the severity of malocclusion and treatment prioritization (Han and Davidson, 2001).

Qualitative methods are convenient in expressing the occlusal traits for classifying the various types of dental malocclusion. Two well-known qualitative methods are Angle’s and British Standard Institute classifications.

 Angle’s classification of malocclusion

This classification was used to define and classify the occlusion based on molar relationship throughout the upper first permanent molar related to the lower first permanent molar which was measured the occlusion by the mesiobuccal cusp of the upper first molar in relation to the mesiobuccal groove of the lower first permanent molar. Angle categorized the malocclusion into 3 classes (Angle, 1899) as following as and shown in (Figure 2.1):

 Class I molar relationship is when the mesiobuccal cusp of upper first permanent molar occludes the mesiobuccal groove of the lower first permanent molar.

 Class II molar relationship is when the mesiobuccal cusp of upper first permanent molar occludes mesially to the mesiobuccal groove of the lower first permanent molar. Class II has subdivided into two divisions based on the inclination of upper incisors i.e. Class II div 1, is when the upper central incisors are proclined and Class II div 2 is when the upper central incisors are retroclined.


 Class III molar relationship is when the mesiobuccal cusp of upper first permanent molar occludes distally to the mesiobuccal groove of the lower first permanent molar.

Figure 2.1 Angel’s molar classification (1899).